N-terminal domain of transcription factor Specificity Protein (SP) 1-4 from arthropods
Specificity Proteins (SPs) are transcription factors that are involved in many cellular processes, including cell differentiation, cell growth, apoptosis, immune responses, response to DNA damage, and chromatin remodeling. There are many SPs in vertebrates (9 SPs in humans and mice, 7 SPs in the chicken, and 11 SPs in teleost fish), but arthropods only have 3 SPs. One SP is clade SP1-4, which is expressed ubiquitously throughout development. SP1-4 belongs to a family of proteins, called the SP/Kruppel or Krueppel-like Factor (KLF) family, characterized by a C-terminal DNA-binding domain of 81 amino acids consisting of three Kruppel-like C2H2 zinc fingers. These factors bind to a loose consensus motif, namely NNRCRCCYY (where N is any nucleotide; R is A/G, and Y is C/T), such as the recurring motifs in GC and GT boxes (5'-GGGGCGGGG-3' and 5-GGTGTGGGG-3') that are present in promoters and more distal regulatory elements of mammalian genes. SP factors preferentially bind GC boxes, while KLFs bind CACCC boxes. Another characteristic hallmark of SP factors is the presence of the Buttonhead (BTD) box CXCPXC, just N-terminal to the zinc fingers. The function of the BTD box is unknown, but it is thought to play an important physiological role. Another feature of most SP factors is the presence of a conserved amino acid stretch, the so-called SP box, located close to the N-terminus. This model represents the N-terminal domain of SP1-4 from arthropods.
Jiyao W et al.(2023). "The conserved domain database in 2023.",